In the course of constructing and maintaining oil and gas wells it is often necessary to convey various types of tools into the well. Many types of conveyance are commonly used as are many types of tools. The most common types of conveyance, in order of increasing cost and decreasing speed of conveyance are: slickline, wireline, coiled tubing, snubbing units, workover rigs, and drilling rigs. The tools used on wells range from very short (under one foot) to arbitrary lengths only limited by the method of putting them in the hole (as high as 3000 feet).
In many cases the well does not have any wellhead pressure when the tools are placed in the well. This type of operation is very quick and simple and the tools are typically supported by slips, a gripping band (also known as a wedding band) or by a C-plate. Slips consists of a set of segments with an external taper and an internal diameter close to the diameter of the tool section. These are placed in a matching tapered slip bowl. The taper combined with the weight of the tool causes them to move inward and grip the tool. With the proper combination of gripping surfaces and tapers the tool will be held reliably. A wedding band has a set of segments that can conform to the outside of the tool and a mechanism to tighten them circumferentially around it. With the correct combination of gripping surfaces and adequate tension in the band, the tool will be held reliably. A C-plate is a large washer with a slot cut through it matching the inside hole. This is slid around the tool and a shoulder on the tool bears on the washer. A keeper is often provided to prevent the tool from moving off of the center line of the C-plate. Once the tool is inside the well, the conveyance system is attached to it and the tool is run into the well.
For wells that have well head pressure, some method of getting the tools connected to the conveyance method and inside the pressure barrier is required. In order of decreasing frequency and increasing difficulty, the current methods are: direct riser deployment, indirect riser deployment, and pressurized connection.
In the first method, a riser is assembled that can contain the entire tool string. In no particular order the riser is assembled, the tool is installed in the riser, and the conveyance method is connected to the tool. Once everything is assembled and attached to the BOPs and the well head, the equipment is pressure and pull tested. Then, the riser pressure is equalized with the well and the well head valves are opened. The tool is then run into the well. The procedure is reversed at the end of the job. This method is quite efficient for short tool strings and for longer tool strings with low force conveyance methods (wireline and slickline) that do not require heavy equipment at the top of the riser. As riser lengths increase and heavy equipment is installed on the top of the riser, this method becomes difficult and dangerous.
The second method splits the tool string into at least two pieces, which may have very different lengths. A riser is used to contain the first tool section. The top of the tool section is provided with a deployment bar with an outside diameter that matches the gripping and sealing diameters of at least one BOP (two may be used at high pressures) and has a connector on the top of it that can be disconnected. Some means must be provided to prevent any well bore fluids from coming through the deployment bar. In the case of purely electrical tools this is easily accomplished. This can be much more difficult in the case of flow through tools. One or more Kelly cocks and/or check valves are used in the case of a single flow through passage. A Kelly cock is an inline ball or plug valve with tool joint threaded ends. In the case of tools with more than one fluid passage, this problem has not been solved.
The first section of the tool is deployed in a manner identical to that of the direct riser method. Once the tool has been lowered such that the deployment bar is located across the appropriate BOP rams, the rams are closed. Pressure and/or pull tests are generally performed. The riser pressure is bled off and the conveyance method is disconnected from the first tool section above the deployment bar (and Kelly cock(s) if present). This disconnection is either accomplished by disconnecting the riser and lifting it to access the connection area or by using a device called a window to safely access the area. A window is a device that can support axial load at all times, but that has a section of the pressure barrier that can be opened and moved out of the way (generally upward) to gain access to the inside.
A special riser with a sliding section is also available that allows the lower section of the riser to be slid upward onto the upper section, thus exposing the connection area without moving the conveyance method. However, this telescoping riser does not carry axial load when it is sliding and it can only contain pressure in its fully extended state. Once the conveyance method is disconnected, any number of additional tool sections may be attached to the conveyance method, installed in the riser, attached to the top of the deployment bar, be deployed, and hung off in the BOPs. The number of tool sections is limited only by the gripping capacity of the BOP (very high), the tensile strength of the deployment bar, and the lifting capacity of the conveyance method (generally the limiting factor).
At this point, a different conveyance method may be used to actually carry the tool down into the well. This is often done in the case of coiled tubing tools as the connection and disconnection step is quite challenging when using coiled tubing. The reasons for this are the residual bend in the coiled tubing pushing the end of the coiled tubing off center, the stiffness of the coiled tubing, and the very high push and pull forces available. Once the tool sections are all in place, the final tool section is attached to the final conveyance method, install in a (usually much shorter) riser, and connected to the deployment bar. Pressure and/or pull tests are generally performed. Once this is done, the riser is equalized with the well head pressure, the BOPs that are holding the deployment bar are opened, and the tool is run down into the well.
This method suffers from many faults. The deployment bars add significant length to the tool string (from 3 feet each to 12 feet each). Many tools are not suitable for deployment bars or special bars have to be designed. Many tools can only be split in certain places leading to long tool sections that have to be deployed. Some tools cannot be used with a Kelly cock. In order for a Kelly cock to be used, the next section of tool must provide a complete pressure barrier above the Kelly cock so that it can be opened with the outside of the tool at atmospheric pressure. One key tool that does not meet this test is a perforating gun. Unfired perforating guns generally do not have a high pressure rated barrier between gun sections, but the gun housing is a very good pressure barrier. Also, the detonating means (generally a detonating cord) must be run all the way through the tool and any deployment bars. Once the guns are fired, they do not provide any pressure barrier at all and any pressure barrier that the deployment bars provided has been exploded. This method also has considerable additional personnel risk due to the possibility of ejecting the tool if the correct steps are not followed in the exact sequence.
The final deployment method is generally very similar to the indirect method. However, the key difference is that a special BOP is provided along with a special connection means, called a CIRP connector. The lower ram of the CIRP BOP can grip the bottom part of a CIRP connector and both locate and support the tool string. The upper ram locks the bottom part of the CIRP connector in place and unlatches the connector. The upper part of the CIRP connector (still attached to the conveyance means) is pulled up and two gate valves are closed, sealing off the well bore. Then, another tool section can be installed in the riser. Once it is in place a pressure and/or pull test is generally performed. The riser pressure is equalized with the well head pressure and the gate valves are opened. The next tool section is conveyed down until the CIPR connector on the bottom of it enters the CIRP connector held in the CIRP BOP. The connector is latched, pull and/or push tested, and the remaining CIRP BOP rams are opened. The tool string is lowered further into the well and the process is repeated at the next connector. This method allows perforating guns to be safely deployed and undeployed since it avoids the need for pressure containing pressure at the deployment section (CIRP connector instead of a deployment bar).
A special method similar to deployment is used in snubbing units. A snubbing unit consists of a fixed slip assembly and a moving slip assembly above it. The moving mechanism is generally capable of providing a very large force in both directions and the two slip assemblies are capable of carrying load in both directions. In these units a ram type BOP is attached to the well head and a special type of BOP called an annular BOP is attached above it. An annular BOP can seal on a variable diameter and allow the object it is sealed on to move through it. It can generally also seal on an open hole, though this consumes a significant portion of the life of the element to do so. Also, it can accommodate variations in the diameter of the object moving through it (such as the upsets on drill pipe). A riser may be provided between the two. The very short tool is inserted through the annular (and possibly the BOP). The upper slip assembly is closed on the drill pipe above the tool. The annular is closed, a pressure test is generally performed, and the well head is opened. The moving mechanism moves the drill pipe downward, forcing the drill pipe through the annular against the wellhead pressure. This procedure is known as snubbing. When the moving mechanism has moved as far as possible, the lower slip is set on the drill pipe. The upper slip is opened and moved upward. The process is repeated.
Additional joints of pipe are torqued on as needed. One or more check valves on the bottom of the drill pipe must hold pressure perfectly if the drill pipe is going to be pumped through. If the drill pipe is only being used as a high force conveyance, the bottom of the drill pipe can be plugged or a sub can be used that doesn't have a hole through it. Snubbing units are very dangerous to operate and the risk of having the drill pipe ejected due to an error in procedure is significant. This procedure is not capable of deploying anything besides very short, simple tools. If a multi-section tool were to be deployed this way, it would have to have a buckling load similar to the drill pipe and have a sufficiently smooth outside diameter for the annular to slide over it. Also, it could not have any sort of protrusions, grooves, holes, soft materials, etc that could damage the annular element. These requirements rule all but the most basic tools.
Accordingly a need exists for a deployment system that allows tools to be deployed into a well in a manner that avoids some or all of the problems associated with existing deployment systems.